Hylobates muelleri

Short phrases consisting of simple hoots and more
complex hoots, short trills, and occasional short quavering notes in males. Quavering
notes are much less pronounced and shorter than in H. lar. Particularly prominent
in this species are short phrases beginning with two or three wa-notes, each slightly
lower in frequency than the preceding one. Short phrases of females almost exclusively
with simple hoots. Some males were heard to produce relatively soft, squealing sounds
between their short phrases, similar to males of H. agilis. Female great call
with an acceleration-type climax, like H. moloch, but with much faster, bubbling
note production (the single notes of the trill are not perceived as such by human
ear), and without becoming slower at the end of the great call. Male optionally produces
coda, sometimes accompanied by female. Male solo song bouts.